The prevalence of gray charges stems from consumers' increasing preference to use debit and credit cards, as well as making online purchases.

Written by

Hadley Malcolm
USA TODAY

Three weeks ago, Mallorie Sullivan, 21, saw her bank account had been overdrawn by about $70 and couldn't figure out why. Until she remembered about a free Amazon Prime trial for students she'd signed up for six months earlier.

The trial had ended, and Amazon automatically converted the Ohio University senior into a paid subscriber. Others interviewed by USA TODAY describe similar experiences with everything from magazine subscriptions to so-called "free" credit reports to video and music streaming services. And it's taking a sizable sum out of their wallets.